U.S. patent application number 16/222198 was filed with the patent office on 2019-07-11 for electrical machine.
This patent application is currently assigned to ROLLS-ROYCE plc. The applicant listed for this patent is ROLLS-ROYCE plc. Invention is credited to Roy S. BARTLE, Rory D. STIEGER.
Application Number | 20190214887 16/222198 |
Document ID | / |
Family ID | 61190371 |
Filed Date | 2019-07-11 |
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United States Patent
Application |
20190214887 |
Kind Code |
A1 |
STIEGER; Rory D. ; et
al. |
July 11, 2019 |
ELECTRICAL MACHINE
Abstract
An electrical machine has a stator carrying electrical windings
which protrude at opposite ends of the stator to form respective,
ring-shaped end windings. The electrical machine further has a
rotor having a plurality of magnetic field-producing elements for
producing a rotor magnetic field which interacts with a stator
magnetic field produced by the windings. The electrical machine
further has a coolant bath for holding liquid coolant. The
electrical machine further has a heat sink in thermal contact with
at least one of the end windings, the bath and the heat sink being
configured such that the heat sink is immersed in the coolant held
in the bath. The heat sink defines one or more fluid pathways
configured such that vapour bubbles, formed when coolant in contact
with the heat sink boils, escape by rising through the heat
sink.
Inventors: |
STIEGER; Rory D.; (Derby,
GB) ; BARTLE; Roy S.; (Isle of Lewis, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROLLS-ROYCE plc |
London |
|
GB |
|
|
Assignee: |
ROLLS-ROYCE plc
London
GB
|
Family ID: |
61190371 |
Appl. No.: |
16/222198 |
Filed: |
December 17, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 7/1823 20130101;
H02K 9/20 20130101; H02K 9/22 20130101; H02K 9/197 20130101; H02K
3/14 20130101; F05D 2220/323 20130101; H02K 3/24 20130101; F28D
15/02 20130101; F01D 15/10 20130101 |
International
Class: |
H02K 9/20 20060101
H02K009/20; F01D 15/10 20060101 F01D015/10; H02K 7/18 20060101
H02K007/18; F28D 15/02 20060101 F28D015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2018 |
GB |
1800167.7 |
Claims
1. An electrical machine having: a stator carrying electrical
windings which protrude at opposite ends of the stator to form
respective, ring-shaped end windings a rotor having a plurality of
magnetic field-producing elements for producing a rotor magnetic
field which interacts with a stator magnetic field produced by the
windings; a coolant bath for holding liquid coolant; and a heat
sink in thermal contact with at least one of the end windings, the
bath and the heat sink being configured such that the heat sink is
immersed in the coolant held in the bath; wherein the heat sink
defines one or more fluid pathways configured such that vapour
bubbles, formed when coolant in contact with the heat sink boils,
escape by rising through the heat sink.
2. The machine according to claim 1, wherein the heat sink
comprises a circumferential row of spaced elongate members which
extend from the end winding into the coolant bath, spaces between
the elongate members providing the fluid pathways.
3. The machine according to claim 1, wherein the heat sink
comprises a ring-shaped foraminous structure which extends from the
end winding into the coolant bath, holes in the foraminous
structure providing the fluid pathways.
4. The machine according to claim 1, wherein the heat sink
comprises a row of vertically-extending, spaced bars which extend
across a face of the end winding, the spaces between the bars
providing the fluid pathways.
5. The machine according to claim 1, further having an intermediary
heat conductor between the end winding and the heat sink.
6. The machine according to claim 5, wherein the intermediary heat
conductor is a ring of electrically insulating material.
7. The machine according to claim 1, wherein the end winding has a
flat end surface for enhanced thermal contact with the heat
sink.
8. The machine according to claim 1, wherein the heat sink is
formed integrally with the end winding.
9. The machine according to claim 1 having a respective heat sink
in thermal contact with each of the end windings, the bath and both
heat sinks being configured such that the heat sinks are immersed
in the coolant.
10. The machine according to claim 1 further having a frame or
casing for holding the heat sink(s) in thermal contact with the end
winding(s).
11. The machine according to claim 1 further having a condenser
operatively connected to the coolant bath for condensing the vapour
formed from the coolant and returning the condensed coolant back to
the coolant bath.
12. A gas turbine engine having an auxiliary drive driven by the
engine and an electrical power generator in turn driven by the
auxiliary drive, the electrical power generator being an electrical
machine according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority from British
Patent Application No. GB 1800167.7, filed on 5 Jan. 2018, the
entire contents of which are incorporated herein by reference.
BACKGROUND
Technical Field
[0002] The present disclosure relates to an electrical machine and
cooling thereof.
Description of the Related Art
[0003] Electrical machines produce heat from resistive losses in
the stator windings. In power dense machines, active cooling of the
stator can be required to avoid material failure from excessive
temperatures.
[0004] The main body of the stator can be cooled using, for
example, a cooling jacket. However, such jackets are generally not
effective for cooling the end windings where the stator windings
protrude from the ends of the stator. In these regions, it has been
proposed to use blown air, or jet impingement of air or liquid.
Another option is to adopt convective cooling of the end windings
by immersing them in a liquid.
[0005] It would be desirable to improve the cooling of stator end
windings.
SUMMARY
[0006] Accordingly, in a first aspect the present disclosure
provides an electrical machine having:
[0007] a stator carrying electrical windings which protrude at
opposite ends of the stator to form respective, ring-shaped end
windings;
[0008] a rotor having a plurality of magnetic field-producing
elements for producing a rotor magnetic field which interacts with
a stator magnetic field produced by the windings;
[0009] a coolant bath for holding liquid coolant; and
[0010] a heat sink in thermal contact with at least one of the end
windings, the bath and the heat sink being configured such that the
heat sink is immersed in the coolant held in the bath;
[0011] wherein the heat sink defines one or more fluid pathways
configured such that vapour bubbles, formed when coolant in contact
with the heat sink boils, escape by rising through the heat
sink.
[0012] The heat sink can increase the surface area available for
heat transfer, improving thermal management of the end winding by
the coolant bath, while helping to avoid any bubbles formed by
boiling coolant developing into a trapped vapour layer (which would
reduce heat transfer).
[0013] The heat sink may advantageously be retrofitted to an
existing machine to improve its thermal performance.
[0014] In a second aspect, the present invention provides a gas
turbine engine having an auxiliary drive driven by the engine and
an electrical power generator in turn driven by the auxiliary
drive, the electrical power generator being an electrical machine
according to the first aspect.
[0015] Optional features of the present disclosure will now be set
out. These are applicable singly or in any combination with any
aspect of the present disclosure.
[0016] The liquid coolant is typically non-electrically conductive.
For example, it can be a fluorinated hydrocarbon such as Novec
7000.TM..
[0017] The magnetic field-producing elements can be permanent
magnets or further windings.
[0018] The heat sink may comprise a circumferential row of spaced
elongate members which extend from the end winding into the coolant
bath, spaces between the elongate members providing the fluid
pathways. For example, the elongate members can be shaped as
cylinders, frustocones or cones. Another option is for the heat
sink to comprise a ring-shaped foraminous, e.g. reticulated,
structure which extends from the end winding into the coolant bath,
holes in the foraminous structure providing the fluid pathways. Yet
another option is for the heat sink to comprise a row of
vertically-extending, spaced bars which extend across a face of the
end winding, the spaces between the bars providing the fluid
pathways.
[0019] The machine may further have an intermediary heat conductor
between the end winding and the heat sink. The intermediary heat
conductor can help to avoid undesirable electromagnetic effects
caused by the proximity of the heat sink to the end winding. For
example, the intermediary heat conductor may be a ring of
electrically insulating material such as e.g. MgO, which can be in
the form of compacted powder. Advantageously, MgO is an electrical
insulator which also has high thermal conductively. Additionally or
alternatively the heat sink may be formed of a dissimilar material
to the windings.
[0020] The end winding may have a flat end surface for enhanced
thermal contact with the heat sink. To facilitate this, the
windings may be formed of, for example, Litz wire, rectangular wire
or conductor bars.
[0021] However, as an alternative, the heat sink may be formed
integrally with the end winding. The thermal contact between the
heat sink and the end winding can then be considerably enhanced.
For example, if the windings are formed of Litz wire, then the heat
sink can be an end portion of the end winding in which passages are
formed in the Litz wire to provide the fluid pathways for escape of
the vapour bubbles. As another example, if the windings are formed
of conductor bars, then the heat sink can be integral projections
from the end winding with passages formed therebetween to provide
the fluid pathways.
[0022] Typically, the machine has a respective heat sink in thermal
contact with each of the end windings, the bath and both heat sinks
being configured such that the heat sinks are immersed in the
coolant.
[0023] The end winding(s) may also be immersed in the coolant.
Indeed, the entire stator windings may be immersed.
[0024] Conveniently, the machine may further have a frame or casing
for holding the heat sink(s) in thermal contact with the end
winding(s).
[0025] The machine may further have a condenser (e.g. a condenser
coil or other type of condenser known to the skilled person)
operatively connected to the coolant bath for condensing the vapour
formed from the coolant and returning the condensed coolant back to
the coolant bath. Conveniently, the condenser function may be
formed in a housing of the electrical machine or it may be a unit
outside such a housing. The condensed coolant may be gravity fed
back to the bath, or its return may be assisted e.g. by a wicking
system or a pump.
DESCRIPTION OF THE DRAWINGS
[0026] Embodiments of the present disclosure will now be described
by way of example with reference to the accompanying drawings in
which:
[0027] FIG. 1 shows a longitudinal cross-section through a ducted
fan gas turbine engine;
[0028] FIG. 2 shows schematically stator windings of an electrical
machine, and a heat sink for an end winding;
[0029] FIG. 3 shows schematically an end view of a variant of the
machine;
[0030] FIG. 4 shows schematically part of the stator windings of
another variant of the machine, the windings having an integral
heat sink for an end winding;
[0031] FIG. 5 shows schematically part of the stator windings of
another variant of the machine, the windings having an integral
heat sink for an end winding; and
[0032] FIG. 6 shows schematically a longitudinal cross-section
through an electrical machine having the stator windings of FIG. 2
and a condenser for condensing coolant vapour.
DETAILED DESCRIPTION
[0033] With reference to FIG. 1, a ducted fan gas turbine engine is
generally indicated at 10 and has a principal and rotational axis
X-X. The engine comprises, in axial flow series, an air intake 11,
a propulsive fan 12, an intermediate pressure compressor 13, a
high-pressure compressor 14, combustion equipment 15, a
high-pressure turbine 16, an intermediate pressure turbine 17, a
low-pressure turbine 18 and a core engine exhaust nozzle 19. A
nacelle 21 generally surrounds the engine 10 and defines the intake
11, a bypass duct 22 and a bypass exhaust nozzle 23.
[0034] During operation, air entering the intake 11 is accelerated
by the fan 12 to produce two air flows: a first air flow A into the
intermediate-pressure compressor 13 and a second air flow B which
passes through the bypass duct 22 to provide propulsive thrust. The
intermediate-pressure compressor 13 compresses the air flow A
directed into it before delivering that air to the high-pressure
compressor 14 where further compression takes place.
[0035] The compressed air exhausted from the high-pressure
compressor 14 is directed into the combustion equipment 15 where it
is mixed with fuel and the mixture combusted. The resultant hot
combustion products then expand through, and thereby drive the
high, intermediate and low-pressure turbines 16, 17, 18 before
being exhausted through the nozzle 19 to provide additional
propulsive thrust. The high, intermediate and low-pressure turbines
respectively drive the high and intermediate-pressure compressors
14, 13 and the fan 12 by suitable interconnecting shafts.
[0036] Other gas turbine engines to which the present disclosure
may be applied may have alternative configurations. By way of
example such engines may have an alternative number of
interconnecting shafts (e.g. two) and/or an alternative number of
compressors and/or turbines. Further the engine may comprise a
gearbox provided in the drive train from a turbine to a compressor
and/or fan.
[0037] The gas turbine engine has one or more associated electrical
machines. For example, an accessory drive powered by an offtake
from one of the interconnecting shafts may in turn power an
electrical generator for providing power to aircraft electrical
systems. Such a generator can also act in reverse operation as a
starter motor.
[0038] The electrical machine has a (typically hollow cylindrical)
stator and associated electrical windings which are typically held
in slots defined between inwardly-directed poles of the stator, and
a rotor located coaxially within the stator and having a plurality
of magnetic field-producing elements, such as permanent magnets or
further windings. These elements produce a rotor magnetic field
which interacts with a stator magnetic field produced by the
windings, whereby the machine operates as an electrical power
generator or electrical motor, depending on the application.
[0039] The stator windings protrude at opposite ends of the stator
to form respective, ring-shaped end windings. In a high power
density machine, the windings may be formed from e.g. Litz wire,
rectangular wire or conductor bars to improve the fill factor of
the windings in the slots. Such a practice also facilitates the
production of end windings with flat external surfaces.
[0040] The electrical machine further has a liquid coolant bath for
holding electrically insulating liquid coolant, such as fluorinated
hydrocarbon, an example being Novec 7000.TM. from 3M. The bath is
used to cool the end windings (as discussed in more detail below),
but it can also be used to cool the entire stator by total
immersion of the stator in the coolant. In this case, seals at
either end of the rotor can prevent the coolant entering the space
inside the stator occupied by the rotor so that the rotor can
rotate in air rather than substantially more viscous liquid.
[0041] At least one, but preferably both, of the end windings has a
respective heat sink in thermal contact the end winding. Heat
produced by resistive losses in an end winding thus flows into its
heat sink, which is immersed in the coolant of the bath. In this
way, the heat produced in the end winding can be efficiently
removed, improving the performance of the machine.
[0042] FIG. 2 shows schematically the stator windings 30, and the
heat sink 31 extending from an end winding thereof. As mentioned
above, another heat sink can extend from the opposite end winding,
but this is not shown in FIG. 2. A ring-shaped intermediary heat
conductor 32 is provided between the end winding and its heat sink
to electrically insulate the heat sink from the windings. In this
way, electromagnetic interference between the heat sink and the
windings can be better avoided. For example the intermediary heat
conductor can be formed of as a gasket of material such as MgO,
e.g. in compacted power form, which is an electrical insulator but
a good conductor of heat. A frame or casing 33 (only a part of
which is shown in FIG. 2) can be provided to hold the heat sink and
intermediary heat conductor against the end winding. Providing the
end winding with a flat external surface can help to promote
intimate contact, and hence enhanced heat transfer, between the end
winding and the intermediary heat conductor.
[0043] As shown in FIG. 2, the heat sink 31 can be formed as a
circumferential row of elongate members 31a (e.g. cylinders,
frustocones or cones) which extend from the end winding into the
coolant bath. These members have spaces therebetween so that vapour
bubbles formed when the coolant boils on contact with the heat sink
can escape by rising through the spaces whatever the orientation of
the machine. Effectively, the spaces provide fluid pathways for the
bubbles. Without such a pathway, trapped bubbles would form a
vapour layer, reducing heat transfer from the heat sink into the
coolant, and ultimately causing undesirable temperature
fluctuations in the end winding.
[0044] Other configurations for the heat sink are possible. For
example, instead of a row of elongate members, the heat sink may be
formed as a foraminous or reticulated ring, in which holes in the
ring provide the fluid pathways for escape of the bubbles. Another
option is shown schematically in FIG. 3, which is an end view of a
variant of the machine in which the entire end of the machine is
covered by a heat sink 31 in the form of a row of substantially
vertically-extending, spaced bars 31b which extend from top to
bottom across the end winding 30a and ultimately join at their ends
to the frame or casing 33. The spaces between the bars provide the
fluid pathways for escape of the bubbles.
[0045] FIGS. 4 and 5 show schematically respective parts of the
stator windings of further variants of the machine. In each of
these variants the windings having an integral heat sink for an end
winding. More particularly, in FIG. 4 the stator windings 30 are
formed from conductor bars. At the end winding 30a, the bars have a
heat sink comprising integral projections 31c from the end winding.
These projections can be staggered to enhance heat transfer, while
creating pathways therebetween for the upwards escape of vapour
bubbles through the heat sink. In FIG. 5, by contrast, the stator
windings 30 are formed from Litz wire. In this case, the integral
heat sink is an end portion of the end winding 30a and the fluid
pathways for escape of vapour bubbles are passages 34 formed in the
Litz wire. The orientation of the passageways can be varied around
the machine relative to the direction of wire so that the
passageways remain approximately vertical.
[0046] By integrating the heat sink with the end winding in this
way, thermal coupling between the heat sink and the end winding can
be enhanced.
[0047] The electrical machine typically has a condenser (e.g. a
condenser coil) for condensing the coolant vapour. For example,
FIG. 6 shows schematically a longitudinal cross-section through an
electrical machine having the stator windings 30 of FIG. 2 and a
condenser 35 for condensing coolant vapour. Also shown are the
machine's rotor 38, stator back iron 39, shaft 40, bearings 41,
slot liner 42, coolant bath 43 and housing 44 for the rotor, stator
and bath. The vapour from the coolant leaves the coolant bath
through a port in an upper part of the housing and then travels to
the condenser through a vapour conduit 36. The condensate returns
to the bath from the condenser through a condensate conduit.
[0048] Although described above in relation to an aero gas turbine
engine, the electrical machine of the present disclosure may be
used in other industrial applications, such as marine and
industrial power generation and drives.
[0049] While the invention has been described in conjunction with
the exemplary embodiments described above, many equivalent
modifications and variations will be apparent to those skilled in
the art when given this disclosure. Accordingly, the exemplary
embodiments of the invention set forth above are considered to be
illustrative and not limiting. Moreover, in determining extent of
protection, due account shall be taken of any element which is
equivalent to an element specified in the claims. Various changes
to the described embodiments may be made without departing from the
scope of the invention.
* * * * *